Wide angle lens system for use in copying machine

ABSTRACT

A wide angle lens system having, from the object side, a first lens of a negative refractive power, a second lens of a positive meniscus lens, a third lens of a negative meniscus lens, a fourth lens of a positive meniscus lens, a diaphragm, a fifth lens being symmetrical with the fourth lens with respect to the diaphragm, a sixth lens being symmetrical with the third lens with respect to the diaphragm, a seventh lens being symmetrical with the second lens with respect to the diaphragm, and a eighth lens being symmetrical with the first lens. Each of the first and eighth lenses may have an aspherical surface in rotation symmetry with each other with respect to the diaphragm. Also, some of the lenses may be made of synthetic resin.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to wide angle lens systems, and moreparticularly to a wide angle lens system for use in copying machines ofthe full exposure type wherein the entire surface of a document isexposed to light at a time to project the light reflected from thesurface on a photosensitive member.

2. Description of the Related Art

The document exposure systems for copying machines heretofore known arethose of the slit exposure type and those of the full exposure type.With the slit exposure type, the photosensitive member is continuouslyexposed to an image of the document in the form of a slit using aprojection lens system which can be relatively narrow in the angle ofview, whereas the machines of this type have the drawback of beingrelatively low in copying speed since the entire surface of the documentmust be exposed to light by a scanning movement. On the other hand, thefull exposure type is adapted for a high-speed copying operation sincethe document need not be scanned, but the projection lens system musthave a very wide angle of view for exposing the photosensitive member tothe entire document image at a time.

Stated more specifically with reference to FIG. 1 showing the fullexposure system for copying machines, an image of a document 1 on adocument support table 2 is projected on a photosensitive belt 3 by aprojection lens system 4. Because of this arrangement, the conjugatedistance L between the document 1 and the photosensitive belt 3 exerts agreat influence on the size of the entire copying machine. To make thecopying machine compact, there is a need to decrease the conjugatedistance L and therefore to give a very wide angle of view to theprojection lens system 4. It is desired that the projection lens system4 to be used be 60 degrees or greater in the angle of view 2ω.

SUMMARY OF THE INVENTION

Accordingly, the main object of the present invention is to provide awide angle lens system having a very wide angle of view and suitable foruse in copying machines of the full exposure type.

Another object of the invention is to provide a wide angle lens systemwhich is bright and compact although having a very wide angle of view.

Another object of the invention is to provide a wide angle lens systemexhibiting satisfactory lens performance over the entire image surface.

Another object of the invention is to provide a wide angle lens systemwhich comprises aspherical lenses, has a wide angle of view andnevertheless exhibits satisfactory lens performance.

Still another object of the invention is to provide a lightweight,compact and inexpensive wide angle lens system comprising lenses ofsynthetic resin.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects or features of the present invention will becomeapparent from the following description of preferred embodiments thereoftaken in conjunction with the accompanying drawings, in which:

FIG. 1 is a diagram showing the construction of the projection opticalsystem of a copying machine of the full exposure type;

FIG. 2 is an optical path diagram showing the paraxial arrangement ofthe projection optical system of FIG. 1;

FIG. 3 is a diagram schematically showing the construction of wide anglelens systems according to the first to third embodiments;

FIGS. 4, 6, 8, 10, 12 and 14 are diagrams respectively showing theconstructions of Examples 1 to 6 included in the first embodiment;

FIGS. 5, 7, 9, 11, 13 and 15 are diagrams respectively showing theaberration curves of Examples 1 to 6;

FIGS. 16, 18, 20 and 22 are diagrams respectively showing theconstructions of Examples 7 to 10 included in the second embodiment;

FIGS. 17, 19, 21 and 23 are diagrams respectively showing the aberrationcurves of Examples 7 to 10;

FIGS. 24 and 26 are diagrams respectively showing Examples 11 and 12included in the third embodiment; and

FIGS. 25 and 27 are diagrams respectively showing the aberration curvesof Examples 11 and 12.

In the following description, like parts are designated by likereference numbers throughout several drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

First to third embodiments of the invention will be described below withreference to the drawings.

FIG. 2 is a diagram showing the paraxial arrangement of the projectionoptical system of FIG. 1 for use in full exposure type copying machines.The projection optical system is perfectly symmetrical with respect to adiaphragm S. Suppose the maximum object length is y (y<0), and thedistance from the object side principal plane H to a document (object) 1is a (a<0), the conversion angle of inclination α0 of the principal rayhaving a maximum angle of view and incident on the lens system isexpressed by the equation (1) below. Indicated at H' in the diagram isthe image side principal plane.

    α0=-y/a(α0<0)                                  (1)

With reference to FIG. 3, the wide angle lens systems of first to thirdembodiments to be described in detail below can be regarded ascomprising, as arranged from the object side toward the image side, anegative lens unit A, positive lens unit B, diaphragm S, positive lensunit B' symmetrical with the lens unit B with respect to the diaphragmS, and negative lens unit A' symmetrical with the lens unit A. When theprincipal ray of maximum angle of view is paraxially traced as anincident ray, the conversion angle of inclination α of the ray incidenton the lens unit B is expressed by the equation (2) given below. It isassumed that the height of incidence on the lens unit A is 1.

    α=α0-φA(α<0)                         (2)

wherein φA is the refracting power (reciprocal of the focal length) ofthe negative lens unit A (A') (φA<0). Since φA<0,

    α-α0=-φA>0                                 (2')

Thus, the absolute value of the conversion angle of inclination α of theray incident on the positive lens unit B is reduced by the action of thenegative lens unit A. Accordingly, the combined lens group of thepositive lens units B and B' arranged symmetrically with each other withrespect to the diaphragm S can be desired with a relatively small angleof view. Further since the object point and the image point will be atan increased distance from the positive lens unit B and the positivelens unit B', respectively, the conjugate distance L can be assumed tobe great relative to the same object length y, hence a great advantageto the correction of aberrations.

FIRST EMBODIMENT

FIGS. 4, 6, 8, 10, 12 and 14 are diagrams respectively showing Examples1 to 6 of wide angle lens systems according to the first embodiment.FIGS. 5, 7, 9, 11, 13 and 15 are diagrams showing the aberration curvesof Examples 1 to 6, respectively.

The lens system of the first embodiment comprises, as arranged from theobject side toward the image side, a first (negative) lens L1, second(positive) lens L2, third (negative) lens L3, fourth (positive) lens L4,diaphragm S, fifth (positive) lens L5, sixth (negative) lens L6, seventh(positive) lens L7 and eighth (negative) lens L8, i.e., eight lenseswhich are arranged symmetrically with respect to the diaphragm S. Theeighth, seventh, sixth and fifth lenses are shaped symmetrically withthe first, second, third and fourth lenses, respectively, with respectto the diaphragm S.

With the first embodiment, the first lens L1 and the eighth lens L8 areeach an aspherical lens having at least one aspherical surface. Thus,the symmetrical lens surfaces of the first lens L1 and the eighth lensL8 are aspherical and in rotation symmetry with each other. As comparedwith the standard curvature, the aspherical surface is preferably soshaped that the refracting power increases in the negative directionwith an increase in the distance from the optical axis.

With the first embodiment, therefore, the first lens L1 corresponds tothe negative lens unit A, the unit of the second lens L2, third lens L3and fourth lens L4 to the positive lens unit B, the unit of the fifthlens L5, sixth lens L6 and seventh lens L7 to the positive lens unit B',and the eighth lens L8 to the negative lens unit A'. Thus, to provide awide angle of view, the first lens L1 and the eighth lens L8 serve asthe respective negative lens units A and A' and are adapted to give adecreased angle of view to the positive lens units B and B'. Thepositive lens units B, B' of the first embodiment described are of theortho-meta type as modified.

The lens system of the first embodiment has a very wide angle of view(about 86° in 2ω) and is yet so compact that it is about 0.38 intelescopic ratio (overall length of lens system/focal length of entiresystem). A technical problem encounted with such wide angle compact lenssystems is the correction of off-axis astigmatic differences. To solvethe technical problem with the first embodiment, aspherical lenses areused as the first lens L1 and the eighth lens L8 which are positioned atthe largest distance from the diaphragm S and with which the positionwhere off-axis rays pass varies greatly with the angle of view.Consequently, off-axis aberrations, especially astigmatic difference andcurvature of field, are corrected satisfactorily. Especially in order toproperly correct the image surface by decreasing Petzval's sum whichdetermines the astigmatic difference, it is desired that the directionof deviation of the aspherical surface from the standard curvature be sodefined that the refracting power increases in the negative directionwith increasing distance from the optical axis.

It is further desired that the following conditional inequality (3) besatisfied by the radius of curvature r4 of the diaphragm side surface ofthe second lens L2 and the radius of curvature r5 of the object side ofthe third lens L3.

    r4>r5                                                      (3)

The inequality (3) is to be satisfied in order to shape the two lensesconcentrically with the diaphragm S and to facilitate the correction ofoff-axis aberrations.

It is further desired that the focal length f1 of the first lens L1 andthe focal length f of the entire lens system satisfy the conditionalinequality (4) below.

    -2.5f<f1<-1.0f                                             (4)

The inequality (4) is to be satisfied to decrease the angle of view ofincident rays on the positive lens unit B and to decrease the overalllength of the lens system. If the focal length f1 is below the lowerlimit value of the inequality (4), the difference between the conversionangles of inclination α and α0 decreases, making it impossible togreatly decrease the angle of view for the positive lens unit B andtherefore presenting difficulty in correcting off-axis aberrations.Beyond the upper limit value, the first lens L1 has too great a negativerefracting power to compact the lens system.

When the first lens L1 and the eighth lens L8 having an asphericalsurface of the largest outside diameter are to be prepared fromsynthetic resin by plastic molding, these lenses can be produced inlarge quantities at a greatly reduced cost.

Tables 1 to 6 show specific numerical values for Examples 1 to 6 shownin FIGS. 4, 6, 8, 10, 12 and 14, respectively.

Each of these tables, (a) shows numerical values for the lens surfacesconcerned, i.e., radii of curvature, axial distances, refractive indexesalong d line and Abbe numbers. The aspherical lens surface is identifiedas such by an asterisk attached to the radius of curvature thereof. Eachtable, (b) shows the aspherical coefficients of the aspherical surfacesin the example concerned. The aspherical coefficient Ai in the table isa coefficient of the function x=f(y, z) representing the asphericalsurface and obtained by plotting the optical axis as x-axis and plottingy-axis and z-axis of orthogonal coordinates in the plane of x=0. When y²+z² =φ², the function is expressed by the equation (5): ##EQU1## whereinCo is the reciprocal of the radius of curvature.

The first and eighth lenses are made of glass in Examples 1 to 4, orsynthetic resin in Examples 5 and 6.

According to the first embodiment described above, a compact wide anglelens system can be realized which exhibits very excellent performance inprojecting images each with a satisfactory quality in its entiretyalthough having an extremely wide angle of view.

                  TABLE 1(a)                                                      ______________________________________                                        [Example 1; FIGS. 4 and 5]                                                    f = 140.1 F No. = 10.0                                                        Radius of  Axial      Refractive  Abbe                                        curvature  distance   index (Nd)  number (νd)                              ______________________________________                                        r.sub.1*                                                                           -353.627                                                                                d.sub.1                                                                              2.260 N.sub.1                                                                            1.59551                                                                              ν.sub.1                                                                         39.23                            r.sub.2 *                                                                          267.305                                                                                 d.sub.2                                                                              1.307                                                   r.sub.3                                                                            30.696                                                                                  d.sub.3                                                                              7.300 N.sub.2                                                                            1.76500                                                                              ν.sub.2                                                                         46.25                            r.sub.4                                                                            57.411                                                                                  d.sub.4                                                                              1.963                                                   r.sub.5                                                                            39.567                                                                                  d.sub.5                                                                              2.404 N.sub.3                                                                            1.68300                                                                              ν.sub.3                                                                         31.52                            r.sub.6                                                                            23.036                                                                                  d.sub.6                                                                              2.767                                                   r.sub.7                                                                            60.748                                                                                  d.sub.7                                                                              3.426 N.sub.4                                                                            1.71700                                                                              ν.sub.4                                                                         47.86                            r.sub.8                                                                            128.142                                                                                 d.sub.8                                                                              5.241                                                   S    --                                                                                      d.sub.9                                                                              5.241                                                   r.sub.9                                                                            -128.142                                                                                d.sub.10                                                                             3.426 N.sub.5                                                                            1.71700                                                                              ν.sub.5                                                                         47.86                            r.sub.10                                                                           -60.748                                                                                 d.sub.11                                                                             2.767                                                   r.sub.11                                                                           -23.036                                                                                 d.sub.12                                                                             2.404 N.sub.6                                                                            1.68300                                                                              ν.sub.6                                                                         31.52                            r.sub.12                                                                           -39.567                                                                                 d.sub.13                                                                             1.963                                                   r.sub.13                                                                           -57.411                                                                                 d.sub.14                                                                             7.300 N.sub.7                                                                            1.76500                                                                              ν.sub.7                                                                         46.25                            r.sub.14                                                                           -30.696                                                                                 d.sub.15                                                                             1.307                                                   r.sub.15 *                                                                         -267.305                                                                                d.sub.16                                                                             2.260 N.sub.8                                                                            1.59551                                                                              ν.sub.8                                                                         39.23                            r.sub.16 *                                                                         353.627                                                                           Σd = 53.337                                                    ______________________________________                                    

                                      TABLE 1(b)                                  __________________________________________________________________________    [Example 1]                                                                   Aspherical coefficient                                                        __________________________________________________________________________    r.sub.1 :                                                                        A.sub.2 =                                                                          0.0      A.sub.3 =                                                                          0.0      A.sub.4 =                                                                         -0.31552 × 10.sup.-7                    A.sub.5 =                                                                          0.0      A.sub.6 =                                                                         -0.73194 × 10.sup.-11                                                             A.sub.7 =                                                                          0.0                                          A.sub.8 =                                                                         -0.74588 × 10.sup.-14                                                             A.sub.9 =                                                                          0.0      A.sub.10 =                                                                        0.93016 × 10.sup.-16                    A.sub.11 =                                                                         0.0      A.sub.12 =                                                                         0.0      A.sub.13 =                                                                         0.0                                          A.sub.14 =                                                                         0.0      A.sub.15 =                                                                         0.0      A.sub.16 =                                                                         0.0                                       r.sub.2 :                                                                        A.sub.2 =                                                                          0.0      A.sub.3 =                                                                          0.0      A.sub.4 =                                                                          0.61558 × 10.sup.-18                   A.sub.5 =                                                                          0.0      A.sub.6 =                                                                          0.32911 × 10.sup.-18                                                             A.sub.7 =                                                                          0.0                                          A.sub.8 =                                                                          0.46912 × 10.sup.-19                                                             A.sub.9 =                                                                          0.0      A.sub.10 =                                                                         0.42997 × 10.sup.-16                   A.sub.11 =                                                                         0.0      A.sub.12 =                                                                         0.16241 × 10.sup.-18                                                             A.sub.13 =                                                                         0.0                                          A.sub.14 =                                                                         0.0      A.sub.15 =                                                                         0.0      A.sub.16 =                                                                         0.0                                       r.sub.15 :                                                                       A.sub.2 =                                                                          0.0      A.sub.3 =                                                                          0.0      A.sub.4 =                                                                         -0.61558 × 10.sup.-18                   A.sub.5 =                                                                          0.0      A.sub.6 =                                                                         -0.32911 × 10.sup.-18                                                             A.sub.7 =                                                                          0.0                                          A.sub.8 =                                                                         -0.46912 × 10.sup.-19                                                             A.sub.9 =                                                                          0.0      A.sub.10 =                                                                        -0.42997 × 10.sup.-16                   A.sub.11 =                                                                         0.0      A.sub.12 =                                                                        -0.16241 × 10.sup.-18                                                             A.sub.13 =                                                                         0.0                                          A.sub.14 =                                                                         0.0      A.sub.15 =                                                                         0.0      A.sub.16 =                                                                         0.0                                       r.sub.16 :                                                                       A.sub.2 =                                                                          0.0      A.sub.3 =                                                                          0.0      A.sub.4 =                                                                          0.31552 × 10.sup.-7                    A.sub.5 =                                                                          0.0      A.sub.6 =                                                                          0.73194 × 10.sup.-11                                                             A.sub.7 =                                                                          0.0                                          A.sub.8 =                                                                          0.74588 × 10.sup.-14                                                             A.sub.9 =                                                                          0.0      A.sub.10 =                                                                        -0.93016 × 10.sup.-16                   A.sub.11 =                                                                         0.0      A.sub.12 =                                                                         0.0      A.sub.13 =                                                                         0.0                                          A.sub.14 =                                                                         0.0      A.sub.15 =                                                                         0.0      A.sub.16 =                                                                         0.0                                       __________________________________________________________________________

                  TABLE 2(a)                                                      ______________________________________                                        [Example 2; FIGS. 6 and 7]                                                    f = 140.1 F No. = 9.0                                                         Radius of  Axial      Refractive  Abbe                                        curvature  distance   index (Nd)  number (νd)                              ______________________________________                                        r.sub.1 *                                                                          -328.140                                                                                d.sub.1                                                                              2.337 N.sub.1                                                                            1.59551                                                                              ν.sub.1                                                                         39.23                            r.sub.2 *                                                                          268.643                                                                                 d.sub.2                                                                              1.402                                                   r.sub.3                                                                            30.670                                                                                  d.sub.3                                                                              7.166 N.sub.2                                                                            1.76500                                                                              ν.sub.2                                                                         46.25                            r.sub.4                                                                            57.481                                                                                  d.sub.4                                                                              1.960                                                   r.sub.5                                                                            39.596                                                                                  d.sub.5                                                                              2.325 N.sub.3                                                                            1.68300                                                                              ν.sub.3                                                                         31.52                            r.sub.6                                                                            23.039                                                                                  d.sub.6                                                                              2.914                                                   r.sub.7                                                                            60.356                                                                                  d.sub.7                                                                              3.476 N.sub.4                                                                            1.71700                                                                              ν.sub.4                                                                         47.86                            r.sub.8                                                                            129.525                                                                                 d.sub.8                                                                              4.910                                                   S    --                                                                       r.sub.9                                                                            -129.525                                                                                d.sub.10                                                                             3.476 N.sub.5                                                                            1.71700                                                                              ν.sub.5                                                                         47.86                            r.sub.10                                                                           -60.356                                                                                 d.sub.11                                                                             2.914                                                   r.sub.11                                                                           -23.039                                                                                 d.sub.12                                                                             2.325 N.sub.6                                                                            1.68300                                                                              ν.sub.6                                                                         31.52                            r.sub.12                                                                           -39.596                                                                                 d.sub.13                                                                             1.960                                                   r.sub.13                                                                           -57.481                                                                                 d.sub.14                                                                             7.166 N.sub.7                                                                            1.76500                                                                              ν.sub.7                                                                         46.25                            r.sub.14                                                                           -30.670                                                                                 d.sub.15                                                                             1.402                                                   r.sub.15 *                                                                         -268.643                                                                                d.sub.16                                                                             2.337 N.sub.8                                                                            1.59551                                                                              ν.sub.8                                                                         39.23                            r.sub.16 *                                                                         328.140                                                                           Σd = 52.979                                                    ______________________________________                                    

                                      TABLE 2(b)                                  __________________________________________________________________________    [Example 2]                                                                   Aspherical coefficient                                                        __________________________________________________________________________    r.sub.1 :                                                                        A.sub.2 =                                                                          0.0      A.sub.3 =                                                                          0.0      A.sub.4 =                                                                         -0.37343 × 10.sup.-7                    A.sub.5 =                                                                          0.0      A.sub.6 =                                                                         -0.56912 × 10.sup.-11                                                             A.sub.7 =                                                                          0.0                                          A.sub.8 =                                                                         -0.87898 × 10.sup.-14                                                             A.sub.9 =                                                                          0.0      A.sub.10 =                                                                         0.10700 × 10.sup.-15                   A.sub.11 =                                                                         0.0      A.sub.12 =                                                                         0.0      A.sub.13 =                                                                         0.0                                          A.sub.14 =                                                                         0.0      A.sub.15 =                                                                         0.0      A.sub.16 =                                                                         0.0                                       r.sub.2 :                                                                        A.sub.2 =                                                                          0.0      A.sub.3 =                                                                          0.0      A.sub.4 =                                                                          0.15866 × 10.sup.-17                   A.sub.5 =                                                                          0.0      A.sub.6 =                                                                          0.47804 × 10.sup.- 18                                                            A.sub.7 =                                                                          0.0                                          A.sub.8 =                                                                          0.65249 × 10.sup.-19                                                             A.sub.9 =                                                                          0.0      A.sub.10 =                                                                         0.46250 × 10.sup.-16                   A.sub.11 =                                                                         0.0      A.sub.12 =                                                                         0.20345 × 10.sup.-18                                                             A.sub.13 =                                                                         0.0                                          A.sub.14 =                                                                         0.0      A.sub.15 =                                                                         0.0      A.sub.16 =                                                                         0.0                                       r.sub.15 :                                                                       A.sub.2 =                                                                          0.0      A.sub.3 =                                                                          0.0      A.sub.4 =                                                                         -0.15866 × 10.sup.-17                   A.sub.5 =                                                                          0.0      A.sub.6 =                                                                         -0.47804 × 10.sup.-18                                                             A.sub.7 =                                                                          0.0                                          A.sub.8 =                                                                         -0.65249 × 10.sup.-19                                                             A.sub.9 =                                                                          0.0      A.sub.10 =                                                                        -0.46250 × 10.sup.-16                   A.sub.11 =                                                                         0.0      A.sub.12 =                                                                        -0.20345 × 10.sup.-18                                                             A.sub.13  =                                                                        0.0                                          A.sub.14 =                                                                         0.0      A.sub.15 =                                                                         0.0      A.sub.16 =                                                                         0.0                                       r.sub.16 :                                                                       A.sub.2 =                                                                          0.0      A.sub.3 =                                                                          0.0      A.sub.4 =                                                                          0.37343 × 10.sup.-7                    A.sub.5 =                                                                          0.0      A.sub.6 =                                                                          0.56912 × 10.sup.-11                                                             A.sub.7 =                                                                          0.0                                          A.sub.8 =                                                                          0.87898 × 10.sup.-14                                                             A.sub.9 =                                                                          0.0      A.sub.10 =                                                                        -0.10700 × 10.sup.-15                   A.sub.11 =                                                                         0.0      A.sub.12 =                                                                         0.0      A.sub.13 =                                                                         0.0                                          A.sub.14 =                                                                         0.0      A.sub.15 =                                                                         0.0      A.sub.16 =                                                                         0.0                                       __________________________________________________________________________

                  TABLE 3(a)                                                      ______________________________________                                        [Example 3; FIGS. 8 and 9]                                                    f = 140.1 F No. = 8.0                                                         Radius of  Axial      Refractive  Abbe                                        curvature  distance   index (Nd)  number (νd)                              ______________________________________                                        r.sub.1 *                                                                          -289.649                                                                                d.sub.1                                                                              2.328 N.sub.1                                                                            1.59551                                                                              ν.sub.1                                                                         39.23                            r.sub.2 *                                                                          269.528                                                                                 d.sub.2                                                                              1.394                                                   r.sub.3                                                                            30.647                                                                                  d.sub.3                                                                              7.084 N.sub.2                                                                            1.76500                                                                              ν.sub.2                                                                         46.25                            r.sub.4                                                                            57.742                                                                                  d.sub.4                                                                              1.996                                                   r.sub.5                                                                            39.502                                                                                  d.sub.5                                                                              2.131 N.sub.3                                                                            1.68300                                                                              ν.sub.3                                                                         31.52                            r.sub.6                                                                            23.066                                                                                  d.sub.6                                                                              3.101                                                   r.sub.7                                                                            59.905                                                                                  d.sub.7                                                                              4.336 N.sub.4                                                                            1.71700                                                                              ν.sub.4                                                                         47.86                            r.sub.8                                                                            131.097                                                                                 d.sub.8                                                                              4.207                                                   S    --                                                                                      d.sub.9                                                                              4.207                                                   r.sub.9                                                                            -131.097                                                                                d.sub.10                                                                             4.336 N.sub.5                                                                            1.71700                                                                              ν.sub.5                                                                         47.86                            r.sub.10                                                                           -59.905                                                                                 d.sub.11                                                                             3.101                                                   r.sub.11                                                                           -23.066                                                                                 d.sub.12                                                                             2.131 N.sub.6                                                                            1.68300                                                                              ν.sub.6                                                                         31.52                            r.sub.12                                                                           - 39.502                                                                                d.sub.13                                                                             1.996                                                   r.sub.13                                                                           -57.742                                                                                 d.sub.14                                                                             7.084 N.sub.7                                                                            1.76500                                                                              ν.sub.7                                                                         46.25                            r.sub.14                                                                           -30.647                                                                                 d.sub.15                                                                             1.394                                                   r.sub.15 *                                                                         -269.528                                                                                d.sub.16                                                                             2.328 N.sub.8                                                                            1.59551                                                                              ν.sub.8                                                                         39.23                            r.sub.16 *                                                                         289.649                                                                           Σd = 53.153                                                    ______________________________________                                    

                                      TABLE 3(b)                                  __________________________________________________________________________    [Example 3]                                                                   Aspherical coefficient                                                        __________________________________________________________________________    r.sub.1 :                                                                        A.sub.2 =                                                                          0.0      A.sub.3 =                                                                          0.0      A.sub.4 =                                                                         -0.43312 × 10.sup.-7                    A.sub.5 =                                                                          0.0      A.sub.6 =                                                                          0.40841 × 10.sup.-11                                                             A.sub.7 =                                                                          0.0                                          A.sub.8 =                                                                          0.79250 × 10.sup.-15                                                             A.sub.9 =                                                                          0.0      A.sub.10 =                                                                         0.11093 × 10.sup.-15                   A.sub.11 =                                                                         0.0      A.sub.12 =                                                                         0.0      A.sub.13 =                                                                         0.0                                          A.sub.14 =                                                                         0.0      A.sub.15 =                                                                         0.0      A.sub.16 =                                                                         0.0                                       r.sub.2 :                                                                        A.sub.2 =                                                                          0.0      A.sub.3 =                                                                          0.0      A.sub.4 =                                                                          0.12169 × 10.sup.-17                   A.sub.5 =                                                                          0.0      A.sub.6 =                                                                          0.49885 × 10.sup.- 18                                                            A.sub.7 =                                                                          0.0                                          A.sub.8 =                                                                          0.70215 × 10.sup.-19                                                             A.sub.9 =                                                                          0.0      A.sub.10 =                                                                         0.55175 × 10.sup.-16                   A.sub.11 =                                                                         0.0      A.sub.12 =                                                                         0.25278 × 10.sup.-18                                                             A.sub.13 =                                                                         0.0                                          A.sub.14 =                                                                         0.0      A.sub.15 =                                                                         0.0      A.sub.16 =                                                                         0.0                                       r.sub.15 :                                                                       A.sub.2 =                                                                          0.0      A.sub.3 =                                                                          0.0      A.sub.4 =                                                                         -0.12169 × 10.sup.-17                   A.sub.5 =                                                                          0.0      A.sub.6 =                                                                         -0.49885 × 10.sup.-18                                                             A.sub.7 =                                                                          0.0                                          A.sub.8 =                                                                         -0.70215 × 10.sup.-19                                                             A.sub.9 =                                                                          0.0      A.sub.10 =                                                                        -0.55175 × 10.sup.-16                   A.sub.11 =                                                                         0.0      A.sub.12 =                                                                        -0.25278 × 10.sup.-18                                                             A.sub.13  =                                                                        0.0                                          A.sub.14 =                                                                         0.0      A.sub.15 =                                                                         0.0      A.sub.16 =                                                                         0.0                                       r.sub.16 :                                                                       A.sub.2 =                                                                          0.0      A.sub.3 =                                                                          0.0      A.sub.4 =                                                                          0.43312 × 10.sup.-7                    A.sub.5 =                                                                          0.0      A.sub.6 =                                                                         -0.40841 × 10.sup.-11                                                             A.sub.7 =                                                                          0.0                                          A.sub.8 =                                                                         -0.79250 × 10.sup.-15                                                             A.sub.9 =                                                                          0.0      A.sub.10 =                                                                        -0.11093 × 10.sup.-15                   A.sub.11 =                                                                         0.0      A.sub.12 =                                                                         0.0      A.sub.13 =                                                                         0.0                                          A.sub.14 =                                                                         0.0      A.sub.15 =                                                                         0.0      A.sub.16 =                                                                         0.0                                       __________________________________________________________________________

                  TABLE 4(a)                                                      ______________________________________                                        [Example 4; FIGS. 10 and 11]                                                  f = 140.1 F No. = 10.0                                                        Radius of  Axial      Refractive  Abbe                                        curvature  distance   index (Nd)  number (νd)                              ______________________________________                                        r.sub.1 *                                                                          -353.633                                                                                d.sub.1                                                                              2.260 N.sub.1                                                                            1.58400                                                                              ν.sub.1                                                                         31.00                            r.sub.2 *                                                                          267.340                                                                                 d.sub.2                                                                              1.307                                                   r.sub.3                                                                            30.695                                                                                  d.sub.3                                                                              7.300 N.sub.2                                                                            1.76200                                                                              ν.sub.2                                                                         40.36                            r.sub.4                                                                            57.413                                                                                  d.sub.4                                                                              1.963                                                   r.sub.5                                                                            39.566                                                                                  d.sub.5                                                                              2.404 N.sub.3                                                                            1.68300                                                                              ν.sub.3                                                                         31.52                            r.sub.6                                                                            23.036                                                                                  d.sub.6                                                                              2.767                                                   r.sub.7                                                                            60.747                                                                                  d.sub.7                                                                              3.426 N.sub.4                                                                            1.72000                                                                              ν.sub.4                                                                         54.71                            r.sub.8                                                                            126.835                                                                                 d.sub.8                                                                              5.241                                                   S    --                                                                                      d.sub.9                                                                              5.241                                                   r.sub.9                                                                            -126.835                                                                                d.sub.10                                                                             3.426 N.sub.5                                                                            1.72000                                                                              ν.sub.5                                                                         54.71                            r.sub.10                                                                           -60.747                                                                                 d.sub.11                                                                             2.767                                                   r.sub.11                                                                           -23.036                                                                                 d.sub.12                                                                             2.404 N.sub.6                                                                            1.68300                                                                              ν.sub.6                                                                         31.52                            r.sub.12                                                                           - 39.566                                                                                d.sub.13                                                                             1.963                                                   r.sub.13                                                                           -57.413                                                                                 d.sub.14                                                                             7.300 N.sub.7                                                                            1.76200                                                                              ν.sub.7                                                                         40.36                            r.sub.14                                                                           -30.695                                                                                 d.sub.15                                                                             1.307                                                   r.sub.15 *                                                                         -267.340                                                                                d.sub.16                                                                             2.260 N.sub.8                                                                            1.58400                                                                              ν.sub.8                                                                         31.00                            r.sub.16 *                                                                         353.633                                                                           Σd = 53.337                                                    ______________________________________                                    

                                      TABLE 4(b)                                  __________________________________________________________________________    [Example 4]                                                                   Aspherical coefficient                                                        __________________________________________________________________________    r.sub.1 :                                                                        A.sub.2 =                                                                          0.0      A.sub.3 =                                                                          0.0      A.sub.4 =                                                                         -0.31552 × 10.sup.-7                    A.sub.5 =                                                                          0.0      A.sub.6 =                                                                         -0.73194 × 10.sup.-11                                                             A.sub.7 =                                                                          0.0                                          A.sub.8 =                                                                         -0.74588 × 10.sup.-14                                                             A.sub.9 =                                                                          0.0      A.sub.10 =                                                                         0.93016 × 10.sup.-16                   A.sub.11 =                                                                         0.0      A.sub.12 =                                                                         0.0      A.sub.13 =                                                                         0.0                                          A.sub.14 =                                                                         0.0      A.sub.15 =                                                                         0.0      A.sub.16 =                                                                         0.0                                       r.sub.2 :                                                                        A.sub.2 =                                                                          0.0      A.sub.3 =                                                                          0.0      A.sub.4 =                                                                          0.73080 × 10.sup.-18                   A.sub.5 =                                                                          0.0      A.sub.6 =                                                                          0.34386 × 10.sup.- 18                                                            A.sub.7 =                                                                          0.0                                          A.sub.8 =                                                                          0.48860 × 10.sup.-19                                                             A.sub.9 =                                                                          0.0      A.sub.10 =                                                                         0.42997 × 10.sup.-16                   A.sub.11 =                                                                         0.0      A.sub.12 =                                                                         0.16241 × 10.sup.-18                                                             A.sub.13 =                                                                         0.0                                          A.sub.14 =                                                                         0.0      A.sub.15 =                                                                         0.0      A.sub.16 =                                                                         0.0                                       r.sub.15 :                                                                       A.sub.2 =                                                                          0.0      A.sub.3 =                                                                          0.0      A.sub.4 =                                                                         -0.73080 × 10.sup.-18                   A.sub.5 =                                                                          0.0      A.sub.6 =                                                                         -0.34386 × 10.sup.-18                                                             A.sub.7 =                                                                          0.0                                          A.sub.8 =                                                                         -0.48860 × 10.sup.-19                                                             A.sub.9 =                                                                          0.0      A.sub.10 =                                                                        -0.42997 × 10.sup.-16                   A.sub.11 =                                                                         0.0      A.sub.12 =                                                                        -0.16241 × 10.sup.-18                                                             A.sub.13  =                                                                        0.0                                          A.sub.14 =                                                                         0.0      A.sub.15 =                                                                         0.0      A.sub.16 =                                                                         0.0                                       r.sub.16 :                                                                       A.sub.2 =                                                                          0.0      A.sub.3 =                                                                          0.0      A.sub.4 =                                                                          0.31552 × 10.sup.-7                    A.sub.5 =                                                                          0.0      A.sub.6 =                                                                          0.73194 × 10.sup.-11                                                             A.sub.7 =                                                                          0.0                                          A.sub.8 =                                                                          0.74588 × 10.sup.-14                                                             A.sub.9 =                                                                          0.0      A.sub.10 =                                                                        -0.93016 × 10.sup.-16                   A.sub.11 =                                                                         0.0      A.sub.12 =                                                                         0.0      A.sub.13 =                                                                         0.0                                          A.sub.14 =                                                                         0.0      A.sub.15 =                                                                         0.0      A.sub.16 =                                                                         0.0                                       __________________________________________________________________________

                  TABLE 5(a)                                                      ______________________________________                                        [Example 5; FIGS. 12 and 13]                                                  f = 140.1 F No. = 10.0                                                        Radius of  Axial      Refractive  Abbe                                        curvature  distance   index (Nd)  number (νd)                              ______________________________________                                        r.sub.1 *                                                                          -375.697                                                                                d.sub.1                                                                              2.500 N.sub.1                                                                            1.58400                                                                              ν.sub.1                                                                         31.00                            r.sub.2 *                                                                          295.734                                                                                 d.sub.2                                                                              0.600                                                   r.sub.3                                                                            30.758                                                                                  d.sub.3                                                                              7.338 N.sub.2                                                                            1.76200                                                                              ν.sub.2                                                                         40.36                            r.sub.4                                                                            55.308                                                                                  d.sub.4                                                                              1.300                                                   r.sub.5                                                                            39.296                                                                                  d.sub.5                                                                              2.456 N.sub.3                                                                            1.68300                                                                              ν.sub.3                                                                         31.52                            r.sub.6                                                                            23.329                                                                                  d.sub.6                                                                              2.765                                                   r.sub.7                                                                            66.366                                                                                  d.sub.7                                                                              3.426 N.sub.4                                                                            1.72000                                                                              ν.sub.4                                                                         54.71                            r.sub.8                                                                            146.950                                                                                 d.sub.8                                                                              5.268                                                   S    --                                                                                      d.sub.9                                                                              5.268                                                   r.sub.9                                                                            -146.950                                                                                d.sub.10                                                                             3.426 N.sub.5                                                                            1.72000                                                                              ν.sub.5                                                                         54.71                            r.sub.10                                                                           -66.366                                                                                 d.sub.11                                                                             2.765                                                   r.sub.11                                                                           -23.329                                                                                 d.sub.12                                                                             2.456 N.sub.6                                                                            1.68300                                                                              ν.sub.6                                                                         31.52                            r.sub.12                                                                           - 39.296                                                                                d.sub.13                                                                             1.300                                                   r.sub.13                                                                           -55.308                                                                                 d.sub.14                                                                             7.338 N.sub.7                                                                            1.76200                                                                              ν.sub.7                                                                         40.36                            r.sub.14                                                                           -30.758                                                                                 d.sub.15                                                                             0.600                                                   r.sub.15 *                                                                         -295.734                                                                                d.sub.16                                                                             2.500 N.sub.8                                                                            1.58400                                                                              ν.sub.8                                                                         31.00                            r.sub.16 *                                                                         375.697                                                                           Σd = 51.306                                                    ______________________________________                                    

                                      TABLE 5(b)                                  __________________________________________________________________________    [Example 5]                                                                   Aspherical coefficient                                                        __________________________________________________________________________    r.sub.1 :                                                                        A.sub.2 =                                                                          0.0      A.sub.3 =                                                                          0.0      A.sub.4 =                                                                         -0.31643 × 10.sup.-7                    A.sub.5 =                                                                          0.0      A.sub.6 =                                                                         -0.70937 × 10.sup.-11                                                             A.sub.7 =                                                                          0.0                                          A.sub.8 =                                                                         -0.96721 × 10.sup.-14                                                             A.sub.9 =                                                                          0.0      A.sub.10 =                                                                         0.10735 × 10.sup.-15                   A.sub.11 =                                                                         0.0      A.sub.12 =                                                                         0.0      A.sub.13 =                                                                         0.0                                          A.sub.14 =                                                                         0.0      A.sub.15 =                                                                         0.0      A.sub.16 =                                                                         0.0                                       r.sub.2 :                                                                        A.sub.2 =                                                                          0.0      A.sub.3 =                                                                          0.0      A.sub.4 =                                                                          0.65283 × 10.sup.-18                   A.sub.5 =                                                                          0.0      A.sub.6 =                                                                          0.29430 × 10.sup.- 18                                                            A.sub.7 =                                                                          0.0                                          A.sub.8 =                                                                          0.41994 × 10.sup.-19                                                             A.sub.9 =                                                                          0.0      A.sub.10 =                                                                         0.44220 × 10.sup.-16                   A.sub.11 =                                                                         0.0      A.sub.12 =                                                                         0.20208 × 10.sup.-18                                                             A.sub.13 =                                                                         0.0                                          A.sub.14 =                                                                         0.0      A.sub.15 =                                                                         0.0      A.sub.16 =                                                                         0.0                                       r.sub.15 :                                                                       A.sub.2 =                                                                          0.0      A.sub.3 =                                                                          0.0      A.sub.4 =                                                                         -0.65283 × 10.sup.-18                   A.sub.5 =                                                                          0.0      A.sub.6 =                                                                         -0.29430 × 10.sup.-18                                                             A.sub.7 =                                                                          0.0                                          A.sub.8 =                                                                         -0.41994 × 10.sup.-19                                                             A.sub.9 =                                                                          0.0      A.sub.10 =                                                                        -0.44220 × 10.sup.-16                   A.sub.11 =                                                                         0.0      A.sub.12 =                                                                        -0.20208 × 10.sup.-18                                                             A.sub.13  =                                                                        0.0                                          A.sub.14 =                                                                         0.0      A.sub.15 =                                                                         0.0      A.sub.16 =                                                                         0.0                                       r.sub.16 :                                                                       A.sub.2 =                                                                          0.0      A.sub.3 =                                                                          0.0      A.sub.4 =                                                                          0.31643 × 10.sup.-7                    A.sub.5 =                                                                          0.0      A.sub.6 =                                                                          0.70937 × 10.sup.-11                                                             A.sub.7 =                                                                          0.0                                          A.sub.8 =                                                                          0.96721 × 10.sup.-14                                                             A.sub.9 =                                                                          0.0      A.sub.10 =                                                                        -0.10735 × 10.sup.-15                   A.sub.11 =                                                                         0.0      A.sub.12 =                                                                         0.0      A.sub.13 =                                                                         0.0                                          A.sub.14 =                                                                         0.0      A.sub.15 =                                                                         0.0      A.sub.16 =                                                                         0.0                                       __________________________________________________________________________

                  TABLE 6 (a)                                                     ______________________________________                                        [Example 6; FIGS. 14 and 15]                                                  f = 140.1  F No. = 8.0                                                        Radius of     Axial     Refractive                                                                              Abbe                                        curvature     distance  index (Nd)                                                                              number (νd)                              ______________________________________                                        r.sub.1 *                                                                            -312.646                                                                                 d.sub.1                                                                             2.186 N.sub.1                                                                           1.58400                                                                             ν.sub.1                                                                         31.00                            r.sub.2 *                                                                            261.032                                                                                  d.sub.2                                                                             1.285                                                 r.sub.3                                                                              30.741                                                                                   d.sub.3                                                                             7.190 N.sub.2                                                                           1.76200                                                                             ν.sub.2                                                                         40.36                            r.sub.4                                                                              58.754                                                                                   d.sub.4                                                                             2.213                                                 r.sub.5                                                                              39.344                                                                                   d.sub.5                                                                             2.014 N.sub.3                                                                           1.68300                                                                             ν.sub.3                                                                         31.52                            r.sub.6                                                                              23.101                                                                                   d.sub.6                                                                             3.248                                                 r.sub.7                                                                              61.378                                                                                   d.sub.7                                                                             5.282 N.sub.4                                                                           1.72000                                                                             ν.sub.4                                                                         54.71                            r.sub.8                                                                              128.474                                                                                  d.sub.8                                                                             3.902                                                 S      --                                                                                       d.sub.9                                                                             3.902                                                 r.sub.9                                                                              -128.474                                                                                 d.sub.10                                                                            5.282 N.sub.5                                                                           1.72000                                                                             ν.sub.5                                                                         54.71                            r.sub.10                                                                             -61.378                                                                                  d.sub.11                                                                            3.248                                                 r.sub.11                                                                             -23.101                                                                                  d.sub.12                                                                            2.014 N.sub.6                                                                           1.68300                                                                             ν.sub. 6                                                                        31.52                            r.sub.12                                                                             -39.344                                                                                  d.sub.13                                                                            2.213                                                 r.sub.13                                                                             -58.754                                                                                  d.sub.14                                                                            7.190 N.sub.7                                                                           1.76200                                                                             ν.sub.7                                                                         40.36                            r.sub.14                                                                             -30.741                                                                                  d.sub.15                                                                            1.285                                                 r.sub.15 *                                                                           -261.032                                                                                 d.sub.16                                                                            2.186 N.sub.8                                                                           1.58400                                                                             ν.sub.8                                                                         31.00                            r.sub.16 *                                                                           312.646                                                                          Σd = 54.642                                                   ______________________________________                                    

                                      TABLE 6 (b)                                 __________________________________________________________________________    [Example 6]                                                                   Aspherical coefficient                                                        __________________________________________________________________________    r.sub.1 :                                                                        A.sub.2 = 0.0                                                                              A.sub.3 = 0.0                                                                              A.sub.4 = -0.85055 × 10.sup.-7                A.sub.5 = 0.0                                                                              A.sub.6 = 0.39236 × 10.sup.-10                                                       A.sub.7 = 0.0                                       A.sub.8 = -0.29988 × 10.sup.-13                                                      A.sub.9 = 0.0                                                                              A.sub.10 = 0.11059 × 10.sup.-15               A.sub.11 = 0.0                                                                             A.sub.12 = 0.0                                                                             A.sub.13 = 0.0                                      A.sub.14 = 0.0                                                                             A.sub.15 = 0.0                                                                             A.sub.16 = 0.0                                   r.sub.2 :                                                                        A.sub.2 = 0.0                                                                              A.sub.3 = 0.0                                                                              A.sub.4 = 0.67740 × 10.sup.-18                A.sub.5 = 0.0                                                                              A.sub.6 = 0.33808 × 10.sup.-18                                                       A.sub.7 = 0.0                                       A.sub.8 = 0.48368 × 10.sup.-19                                                       A.sub.9 =  0.0                                                                             A.sub.10 = 0.41627 × 10.sup.-16               A.sub.11 = 0.0                                                                             A.sub.12 = 0.21617 × 10.sup.-18                                                      A.sub.13 = 0.0                                      A.sub.14 = 0.0                                                                             A.sub.15 = 0.0                                                                             A.sub.16 = 0.0                                   r.sub.15 :                                                                       A.sub.2 = 0.0                                                                              A.sub.3 = 0.0                                                                              A.sub.4 = -0.67740 × 10.sup.-18               A.sub.5 = 0.0                                                                              A.sub.6 = -0.33808 × 10.sup.-18                                                      A.sub.7 = 0.0                                       A.sub.8 = .sup.-0.48368 × 10.sup.-19                                                 A.sub.9 = 0.0                                                                              A.sub.10 = -0.41627 × 10.sup.-16              A.sub.11 = 0.0                                                                             A.sub.12 = -0.21617 × 10.sup.-18                                                     A.sub.13 = 0.0                                      A.sub.14 = 0.0                                                                             A.sub.15 = 0.0                                                                             A.sub.16 = 0.0                                   r.sub.16 :                                                                       A.sub.2 = 0.0                                                                              A.sub.3 = 0.0                                                                              A.sub.4 = 0.85055 × 10.sup.-7                 A.sub.5 = 0.0                                                                              A.sub.6 = -0.39236 × 10.sup.-10                                                      A.sub.7 = 0.0                                       A.sub.8 = 0.29988 × 10.sup.-13                                                       A.sub.9 = 0.0                                                                              A.sub.10 = -0.11059 × 10.sup.-15              A.sub.11 = 0.0                                                                             A.sub.12 = 0.0                                                                             A.sub.13 = 0.0                                      A.sub.14 = 0.0                                                                             A.sub.15 = 0.0                                                                             A.sub.16 = 0.0                                   __________________________________________________________________________

SECOND EMBODIMENT

FIGS. 16, 18, 20 and 22 are diagrams respectively showing Examples 7 to10 of wide angle lens systems according to the second embodiment. FIGS.17, 19, 21 and 23 are diagrams showing the aberration curves of Examples7 to 10, respectively.

The lens system of the second embodiment comprises, as arranged from theobject side toward the image side, a first lens unit U1 in the form of anegative first lens L11, a second lens unit U2 composed of a positivemeniscus second lens L12 having a convex surface directed toward theobject side and a negative meniscus third lens L13 having a concavesurface directed toward the image side, a third lens unit U3 in the formof a positive meniscus fourth lens L14 having a convex surface directedtoward the object side, a diaphragm S, a fourth lens unit U4 symmetricalwith the third lens unit U3 with respect to the diaphragm S and in theform of a positive meniscus fifth lens L15 with a convex surfacedirected toward the image side, a fifth lens unit U5 symmetrical withthe second lens unit U2 with respect to the diaphragm S and composed ofa negative meniscus sixth lens L16 with a concave surface directedtoward the object side and a positive meniscus seventh lens L17 with aconvex surface directed toward the image side, and a sixth lens unit U6symmetrical with the first lens unit U1 with respect to the diaphragm Sand in the form of a negative eighth lens L18. Thus, the lens systemcomprises eight lenses in six groups as arranged symmetrically withrespect to the diaphragm S. The eighth, seventh, sixth and fifth lensesare shaped symmetrically with the first, second, third and fourthlenses, respectively, with respect to the diaphragm S.

In the second embodiment as in the first, therefore, the first lens L11corresponds to the negative lens unit A, the unit of the second lensL12, third lens L13 and fourth lens L14 to the positive lens unit B, theunit of the fifth lens L15, sixth lens L16 and seventh lens L17 to thepositive lens unit B', and the eighth lens L18 to the negative lens unitA'. Thus, to provide a wide angle of view, the first lens L11 and theeighth lens L18 serve as the respective negative lens units A and A' andare adapted to give a decreased angle of view to the positive lens unitsB and B' As in the case of the first embodiment, the positive lens unitsB, B' of the second embodiment are also the ortho-meta type as modified.

Further in the case of the lens system of the second embodiment, thefollowing conditional inequality (6) is satisfied by the radius ofcurvature r4 of the diaphragm side surface of the second lens L12 andthe radius of curvature r5 of the object side of the third lens L13.

    r4≧r5                                               (6)

The inequality (6) is to be satisfied in order to shape the two lensesconcentrically with the diaphragm S and to facilitate the correction ofoff-axis aberrations.

Further if the diaphragm side surface r6 of the third lens L13 is mademarkedly concave, it is possible to reduce the Petzval's sum tofacilitate the correction of astigmatic difference that is difficult atwide angles of view and to satisfactorily correct the sphericalaberration occurring in the under direction at the object side surfacer3 of the second lens L12.

Furthermore, it is desired that the focal length f1 of the first lensL11 and the focal length f of the entire lens system satisfy theconditional inequality (7) given below.

    -2.5f<f1<-1.0f                                             (7)

The inequality (7), when satisfied, decreases the angle of view ofincident rays on the positive lens unit B and decreases the overalllength of the lens system. If the focal length f1 is below the lowerlimit value of the inequality (7), the difference between the conversionangles of inclination α and α0 decreases, making it impossible togreatly decrease the angle of view for the positive lens unit B andtherefore presenting difficulty in correcting off-axis aberrations.Beyond the upper limit value, the first lens L11 has too great anegative refracting power to compact the lens system. The lens system ofthe second embodiment realizes a wide angle of view (2ω=about 86°) andis yet so compact that it is about 0.35 in telescopic ratio (overalllength of lens system/focal length of entire system).

It is also desired that the following conditional inequality (8) besatisfied by the radius of curvature r3 of the image side surface of thesecond lens L12 and the radius of curvature r6 of the image side of thethird lens L13.

    1.0<r3/r6<1.5                                              (8)

The inequality (8) serves to adequately correct the off-axis astigmaticdifference and is useful especially for correcting this difference onthe meridional side. If the upper limit value of the inequality (8) isexceeded, it becomes difficult to correct the off-axis coma aberration.Beyond the lower limit value, the curvature of field becomes correctedexcessively on the meridional side to result in an increased astigmaticdifference and impair the image surface and the uniformity of images.

It is further desired that the second lens L12 and the third lens L13satisfy the following conditional inequalities (9) and (10):

    N2-N3>0.05                                                 (9)

    ν2-ν3>6.0                                            (10)

wherein N2 and N3 are the refractive indexes of the respective secondand third lenses, and ν2 and ν3 are the Abbe numbers thereof.

The inequality (9), when satisfied, serves to diminish Petzval's sum andhold the image surface planar. The inequality (10) serves tosatisfactorily correct off-axis chromatic aberrations.

Tables 7 to 10 show specific numerical values for Examples 7 to 10 shownin FIGS. 16, 18, 20 and 22, respectively.

In Examples 9 and 10, the second lens unit comprising the second andthird lenses and the fifth lens unit comprising the sixth and seventhlenses are each in the form of a compound lens composed of the twolenses affixed to each other.

The second embodiment described provides a compact lens system whichexhibits very excellent performance in projecting images each with asatisfactory quality in its entirety although having an extremely wideangle of view.

                  TABLE 7                                                         ______________________________________                                        [Example 7; FIGS. 16 and 17]                                                  f = 140.0  F No. = 10.0  2ω = 85.8                                      Radius of     Axial    Refractive Abbe                                        curvature     distance index (Nd) number (νd)                              ______________________________________                                        r.sub.1                                                                              2072.925                                                                                 d.sub.1                                                                             2.5  N.sub.1                                                                            1.59551                                                                             ν.sub.1                                                                         39.23                            r.sub.2                                                                              160.399                                                                                  d.sub.2                                                                             0.2                                                   r.sub.3                                                                              31.075                                                                                   d.sub.3                                                                             7.0  N.sub.2                                                                            1.76500                                                                             ν.sub.2                                                                         46.25                            r.sub.4                                                                              58.629                                                                                   d.sub.4                                                                             2.0                                                   r.sub.5                                                                              33.894                                                                                   d.sub.5                                                                             2.0  N.sub.3                                                                            1.68300                                                                             ν.sub.3                                                                         31.52                            r.sub.6                                                                              22.325                                                                                   d.sub.6                                                                             3.0                                                   r.sub.7                                                                              64.530                                                                                   d.sub.7                                                                             3.1  N.sub.4                                                                            1.72000                                                                             ν.sub.4                                                                         52.14                            r.sub.8                                                                              98.811                                                                                   d.sub.8                                                                             5.0                                                   S      --                                                                                       d.sub.9                                                                             5.0                                                   r.sub.9                                                                              -98.811                                                                                  d.sub.10                                                                            3.1  N.sub.5                                                                            1.72000                                                                             ν.sub.5                                                                         52.14                            r.sub.10                                                                             -64.530                                                                                  d.sub.11                                                                            3.0                                                   r.sub.11                                                                             -22.325                                                                                  d.sub.12                                                                            2.0  N.sub.6                                                                            1.68300                                                                             ν.sub.6                                                                         31.52                            r.sub.12                                                                             -33.894                                                                                  d.sub.13                                                                            2.0                                                   r.sub.13                                                                             -58.629                                                                                  d.sub.14                                                                            7.0  N.sub.7                                                                            1.76500                                                                             ν.sub.7                                                                         46.25                            r.sub.14                                                                             -31.075                                                                                  d.sub.15                                                                            0.2                                                   r.sub.15                                                                             -160.399                                                                                 d.sub.16                                                                            2.5  N.sub.8                                                                            1.59551                                                                             ν.sub.8                                                                         39.23                            r.sub.16                                                                             -2072.925                                                                         Σd = 49.6                                                    d/f = 0.355  r.sub.4 /r.sub.5 = 1.73                                                                     f.sub.1 /f = -2.09                                 r.sub.3 /r.sub.6 = 1.39                                                                    N.sub.2 -N.sub.3 = 0.082                                                                    ν.sub.2 -ν.sub.3 = 14.73                     ______________________________________                                    

                  TABLE 8                                                         ______________________________________                                        [Example 8; FIGS. 18 and 19]                                                  f = 140.0  F No. = 10.0  2ω = 85.8                                      Radius of     Axial    Refractive Abbe                                        curvature     distance index (Nd) number (νd)                              ______________________________________                                        r.sub.1                                                                              -703.838                                                                                 d.sub.1                                                                             2.5  N.sub.1                                                                            1.59551                                                                             ν.sub.1                                                                         39.23                            r.sub.2                                                                              262.180                                                                                  d.sub.2                                                                             0.2                                                   r.sub.3                                                                              30.813                                                                                   d.sub.3                                                                             7.0  N.sub.2                                                                            1.76500                                                                             ν.sub.2                                                                         46.25                            r.sub.4                                                                              57.694                                                                                   d.sub.4                                                                             2.0                                                   r.sub.5                                                                              39.169                                                                                   d.sub.5                                                                             2.0  N.sub.3                                                                            1.68300                                                                             ν.sub.3                                                                         31.52                            r.sub.6                                                                              23.270                                                                                   d.sub.6                                                                             3.0                                                   r.sub.7                                                                              61.902                                                                                   d.sub.7                                                                             3.1  N.sub.4                                                                            1.72000                                                                             ν.sub.4                                                                         52.14                            r.sub.8                                                                              109.469                                                                                  d.sub.8                                                                             5.0                                                   S      --                                                                                       d.sub.9                                                                             5.0                                                   r.sub.9                                                                              -109.469                                                                                 d.sub.10                                                                            3.1  N.sub.5                                                                            1.72000                                                                             ν.sub.5                                                                         52.14                            r.sub.10                                                                             -61.902                                                                                  d.sub.11                                                                            3.0                                                   r.sub.11                                                                             -23.270                                                                                  d.sub.12                                                                            2.0  N.sub.6                                                                            1.68300                                                                             ν.sub.6                                                                         31.52                            r.sub.12                                                                             -39.169                                                                                  d.sub.13                                                                            2.0                                                   r.sub.13                                                                             -57.694                                                                                  d.sub.14                                                                            7.0  N.sub.7                                                                            1.76500                                                                             ν.sub.7                                                                         46.25                            r.sub.14                                                                             -30.813                                                                                  d.sub.15                                                                            0.2                                                   r.sub.15                                                                             -262.180                                                                                 d.sub.16                                                                            2.5  N.sub.8                                                                            1.59551                                                                             ν.sub.8                                                                         39.23                            r.sub.16                                                                             703.838                                                                           Σd = 49.6                                                    d/f = 0.355  r.sub.4 /r.sub.5 = 1.47                                                                     f.sub.1 /f = -2.29                                 r.sub.3 /r.sub.6 = 1.32                                                                    N.sub.2 -N.sub.3 = 0.082                                                                    ν.sub.2 -ν.sub.3 = 14.73                     ______________________________________                                    

                  TABLE 9                                                         ______________________________________                                        [Example 9; FIGS. 20 and 21]                                                  f = 140.0  F No. = 10.0  2ω = 85.8                                      Radius of      Axial    Refractive                                                                              Abbe                                        curvature      distance index (Nd)                                                                              number (νd)                              ______________________________________                                        r.sub.1  -352.103                                                                                d.sub.1                                                                              3.2 N.sub.1                                                                           1.59551                                                                             ν.sub.1                                                                         39.23                            r.sub.2  130.436                                                                                 d.sub.2                                                                              1.9                                                 r.sub.3  29.936                                                                                  d.sub.3                                                                              6.4 N.sub.2                                                                           1.77551                                                                             ν.sub.2                                                                         37.90                            r.sub.4 = r.sub.5                                                                      43.583                                                                                  d.sub.4                                                                              3.6 N.sub.3                                                                           1.68300                                                                             ν.sub.3                                                                         31.52                            r.sub.6  24.458                                                                                  d.sub.5                                                                              1.3                                                 r.sub.7  45.773                                                                                  d.sub.6                                                                              2.1 N.sub.4                                                                           1.72000                                                                             ν.sub.4                                                                         52.14                            r.sub.8  208.016                                                                                 d.sub.7                                                                              4.0                                                 S        --                                                                                      d.sub.8                                                                              4.0                                                 r.sub.9  -208.016                                                                                d.sub.9                                                                              2.1 N.sub.5                                                                           1.72000                                                                             ν.sub.5                                                                         52.14                            r.sub.10 -45.773                                                                                 d.sub.10                                                                             1.3                                                 r.sub.11 -24.458                                                                                 d.sub.11                                                                             3.6 N.sub.6                                                                           1.68300                                                                             ν.sub. 6                                                                        31.52                            r.sub.12 = r.sub.13                                                                    -43.583                                                                                 d.sub.12                                                                             6.4 N.sub.7                                                                           1.77551                                                                             ν.sub.7                                                                         37.90                            r.sub.14 -29.936                                                                                 d.sub.13                                                                             1.9                                                 r.sub.15 -130.436                                                                                d.sub.14                                                                             3.2 N.sub.8                                                                           1.59551                                                                             ν.sub.8                                                                         39.23                            r.sub.16 352.103                                                                           Σd.sub. = 45.0                                             d/f = 0.321  r.sub.4 /r.sub.5 = 1.00                                                                     f.sub.1 /f = -1.139                                r.sub.3 /r.sub.6 = 1.22                                                                    N.sub.2 -N.sub.3 = 0.093                                                                    ν.sub.2 -ν.sub.3 = 6.38                      ______________________________________                                    

                  TABLE 10                                                        ______________________________________                                        [Example 10; FIGS. 22 and 23]                                                 f = 140.0  F No. = 10.0  2ω = 85.8                                      Radius of      Axial    Refractive                                                                              Abbe                                        curvature      distance index (Nd)                                                                              number (νd)                              ______________________________________                                        r.sub.1  477.167                                                                                 d.sub.1                                                                              3.2 N.sub.1                                                                           1.59551                                                                             ν.sub.1                                                                         39.23                            r.sub.2  117.959                                                                                 d.sub.2                                                                              1.9                                                 r.sub.3  33.095                                                                                  d.sub.3                                                                              6.4 N.sub.2                                                                           1.78560                                                                             ν.sub.2                                                                         42.81                            r.sub.4 = r.sub.5                                                                      45.366                                                                                  d.sub.4                                                                              3.6 N.sub.3                                                                           1.64796                                                                             ν.sub.3                                                                         31.23                            r.sub.6  27.473                                                                                  d.sub.5                                                                              1.3                                                 r.sub.7  50.058                                                                                  d.sub.6                                                                              2.1 N.sub.4                                                                           1.75450                                                                             ν.sub.4                                                                         51.57                            r.sub.8  119.780                                                                                 d.sub.7                                                                              4.0                                                 S        --                                                                                      d.sub.8                                                                              4.0                                                 r.sub.9  -119.780                                                                                d.sub.9                                                                              2.1 N.sub.5                                                                           1.75450                                                                             ν.sub.5                                                                         51.57                            r.sub.10 -50.058                                                                                 d.sub.10                                                                             1.3                                                 r.sub.11 -27.473                                                                                 d.sub.11                                                                             3.6 N.sub.6                                                                           1.64769                                                                             ν.sub.6                                                                         31.23                            r.sub.12 = r.sub.13                                                                    -45.366                                                                                 d.sub.12                                                                             6.4 N.sub.7                                                                           1.78560                                                                             ν.sub.7                                                                         42.81                            r.sub.14 -33.095                                                                                 d.sub.13                                                                             1.9                                                 r.sub.15 -117.959                                                                                d.sub.14                                                                             3.2 N.sub.8                                                                           1.59551                                                                             ν.sub.8                                                                         39.23                            r.sub.16 -477.167                                                                          Σd = 45.0                                                  d/f = 0.321  r.sub.4 /r.sub.5 = 1.00                                                                     f.sub.1 /f = -1.885                                r.sub.3 /r.sub.6 = 1.20                                                                    N.sub.2 -N.sub.3 = 0.093                                                                    ν.sub.2 -ν.sub.3 = 11.58                     ______________________________________                                    

THIRD EMBODIMENT

FIGS. 24 and 26 respectively show Examples 11 and 12 of wide angle lenssystems according to the third embodiment. FIGS. 25 and 27 show theaberration curves of Examples 11 and 12, respectively.

The wide angle lens system of the third embodiment is similar inconstruction to the system of the second embodiment and comprises, asarranged from the object side toward the image side, a negative firstlens L21, positive meniscus second lens L22 with a convex surfacedirected toward the object side, negative meniscus third lens L23 with aconcave surface directed toward the image side, positive meniscus fourthlens L24 with a convex surface directed toward the object side,diaphragm S, positive meniscus fifth lens L25 symmetrical with thefourth lens L24 with respect to the diaphragm S and having a convexsurface directed toward the image side, negative meniscus sixth lens L26symmetrical with the third lens L23 with respect to the diaphragm S andhaving a concave surface directed toward the object side, positivemeniscus seventh lens L27 symmetrical with the second lens L22 withrespect to the diaphragm S and having a convex surface directed towardthe image side, and negative eighth lens L28 symmetrical with the firstlens L21 with respect to the diaphragm S. With the third embodiment,synthetic resin is used for making the negative first lens L21, positivemeniscus fourth lens L24 with its convex surface directed toward theobject side, positive meniscus fifth lens L25 with its convex surfacedirected toward the image side and negative eighth lens L28.

In the third embodiment as in the above embodiments, therefore, thefirst lens L21 corresponds to the negative lens unit A, the unit of thesecond lens L22, third lens L23 and fourth lens L24 to the positive lensunit B, the unit of the fifth lens L25, sixth lens L26 and seventh lensL27 to the positive lens unit B', and the eighth lens L28 to thenegative lens unit A'. Thus, to provide a wide angle of view, the firstlens L21 and the eighth lens L28 serve as the respective negative lensunits A and A' and are adapted to give a decreased angle of view to thepositive lens units B and B'.

Further with the third embodiment, the shift of the image point due tovariations in temperature and peculiar to lens systems of syntheticresin is corrected by using a negative lens of polycarbonate or likeresin as each of the first lens L21 and the eighth lens L28, and alsousing a positive lens of acrylic or like resin as each of the fourthlens L24 and the fifth lens L25. This collectively offsets variations inthe focal lengths of the individual lenses. Since polycarbonate resinand acrylic resin are at the same level in respect of coefficient oflinear expansion and variation coefficient of refractive index, it isdesired that the focal length f1 of the first lens L21 and the focallength f4 of the fourth lens L24 satisfy the following conditionalinequality (11).

    -1.60<f1/f4<-0.95                                          (11)

If the ratio f1/f4 is outside the range defined by the inequality (11),the image point shifts by at least 0.20 mm for a temperature variationof ±10° C. from the ambient temperature 20° C.

With the lens system of the third embodiment, it is desired that theradius of curvature r4 of the diaphragm side surface of the second lensL22 and the radius of curvature r5 of the object side of the third lensL23 satisfy the following conditional inequality (12) which is the sameas the inequality (6) described with reference to the second embodiment.

    r4≧r5                                               (12)

It is also desired that the radius of curvature r3 of the image sidesurface of the second lens L22 and the radius of curvature r6 of theimage side of the third lens L23 satisfy the following conditionalinequality (13) which is the same as the inequality (8) described withreference to the second embodiment.

    1.0<r3/r6<1.5                                              (13)

It is further desired that the second lens L22 and the third lens L23satisfy the following inequalities (14), (15) which are the same as theinequalities (9), (10), respectively.

    N2-N3>0.05 (N7-N6>0.05)                                    (14)

    ν2-ν3>6.0 (ν7-ν6>6.0)                          (15)

wherein N2 and N3 are the refractive indexes of the respective secondand third lenses, and ν2 and ν3 are the Abbe numbers thereof.

In the case of the third embodiment as in the first embodiment, each ofthe first lens L21 and the eighth lens L28 may have at least oneaspherical surface. In this case, the symmetrical lens surfaces of thefirst lens L21 and the eighth lens L28 are aspherical and in rotationsymmetry with each other. The aspherical surface is preferably so shapedthat as compared with the standard curvature, the refracting powerincreases in the negative direction with increasing distance from theoptical axis, whereby the astigmatic difference can be corrected moreefficiently.

Table 11 and Tables 12,(a) and (b) give specific numerical values forExamples 11 and 12 shown in FIGS. 24 and 26, respectively. Theaspherical coefficients Ai in Table 12 (b) are defined by the foregoingequation (5).

All the lenses of Example 11 are spherical, while the first lens and theeighth lens of Example 12 are aspherical. In these examples, the firstand eighth lenses are made of polycarbonate resin, and the fourth andfifth lenses are made of acrylic resin.

The third embodiment described above also realizes a wide angle lenssystem which is as compact as about 0.34 in telescopic ratio (overalllength of lens system/focal length of entire system) although having avery wide angle of view (2ω=about 86°) and which exhibits exceedinglyexcellent performance in projecting images each with a satisfactoryquality in its entirety. Of the eight component lenses, four lenses aremade of synthetic resin, so that the wide angle lens system islightweight and diminished in the likelihood of the image point shiftingat varying temperatures.

In the foregoing description of the first to third embodiments, theconditional inequalities (3), (4) and (6) to (15) have been describedwith reference to the lenses positioned on the object side of thediaphragm. However, since the wide angle lens systems of the embodimentsare symmetrical with respect to the diaphragm, it is to be noted thatthe lenses on the image side of the diaphragm of course similarlysatisfy such inequalities.

                  TABLE 11                                                        ______________________________________                                        [Examp1e 11; FIGS. 24 and 25]                                                 f = 140.0  F No. = 10.0  2ω = 85.8                                      Radius of     Axial    Refractive Abbe                                        curvature     distance index (Nd) number (νd)                              ______________________________________                                        r.sub.1                                                                              -714.20                                                                                  d.sub.1                                                                             2.5  N.sub.1                                                                            1.5840                                                                              ν.sub.1                                                                         31.0                             r.sub.2                                                                              256.21                                                                                   d.sub.2                                                                             0.6                                                   r.sub.3                                                                              26.72                                                                                    d.sub.3                                                                             6.5  N.sub.2                                                                            1.7440                                                                              ν.sub.2                                                                         44.9                             r.sub.4                                                                              45.53                                                                                    d.sub.4                                                                             0.8                                                   r.sub.5                                                                              28.40                                                                                    d.sub.5                                                                             2.2  N.sub.3                                                                            1.6830                                                                              ν.sub.3                                                                         31.5                             r.sub.6                                                                              19.15                                                                                    d.sub.6                                                                             3.6                                                   r.sub.7                                                                              67.33                                                                                    d.sub.7                                                                             3.2  N.sub.4                                                                            1.4914                                                                              ν.sub.4                                                                         57.8                             r.sub.8                                                                              144.47                                                                                   d.sub.8                                                                             4.5                                                   S      --                                                                                       d.sub.9                                                                             4.5                                                   r.sub.9                                                                              -144.47                                                                                  d.sub.10                                                                            3.2  N.sub.5                                                                            1.4914                                                                              ν.sub.5                                                                         57.8                             r.sub.10                                                                             -67.33                                                                                   d.sub.11                                                                            3.6                                                   r.sub.11                                                                             -19.15                                                                                   d.sub.12                                                                            2.2  N.sub.6                                                                            1.6830                                                                              ν.sub.6                                                                         31.5                             r.sub.12                                                                             -28.40                                                                                   d.sub.13                                                                            0.8                                                   r.sub.13                                                                             -45.53                                                                                   d.sub.14                                                                            6.5  N.sub.7                                                                            1.7440                                                                              ν.sub.7                                                                         44.9                             r.sub.14                                                                             -26.72                                                                                   d.sub.15                                                                            0.6                                                   r.sub.15                                                                             -256.21                                                                                  d.sub.16                                                                            2.5  N.sub.8                                                                            1.5840                                                                              ν.sub.8                                                                         31.0                             r.sub.16                                                                             714.20                                                                            Σd = 47.8                                                    f.sub.1 /f.sub.4 = -1.274                                                                         r.sub.3 /r.sub.6 = 1.40                                   N.sub.2 -N.sub.3 = 0.061                                                                          ν.sub.2 -ν.sub.3 = 13.41                            ______________________________________                                    

                  TABLE 12 (a)                                                    ______________________________________                                        [Examp1e 12; FIGS. 26 and 27]                                                 f = 140.1  F No. = 10.0  2ω = 85.8                                      Radius of     Axial    Refractive Abbe                                        curvature     distance index (Nd) number (νd)                              ______________________________________                                        r.sub.1 *                                                                            -2668.30                                                                                 d.sub.1                                                                             2.5  N.sub.1                                                                            1.5840                                                                              ν.sub.1                                                                         31.0                             r.sub.2 *                                                                            226.47                                                                                   d.sub.2                                                                             0.6                                                   r.sub.3                                                                              26.76                                                                                    d.sub.3                                                                             6.5  N.sub.2                                                                            1.7440                                                                              ν.sub.2                                                                         44.9                             r.sub.4                                                                              46.13                                                                                    d.sub.4                                                                             0.8                                                   r.sub.5                                                                              29.83                                                                                    d.sub.5                                                                             2.2  N.sub.3                                                                            1.6830                                                                              ν.sub.3                                                                         31.5                             r.sub.6                                                                              19.53                                                                                    d.sub.6                                                                             3.6                                                   r.sub.7                                                                              63.23                                                                                    d.sub.7                                                                             3.2  N.sub.4                                                                            1.4914                                                                              ν.sub.4                                                                         57.8                             r.sub.8                                                                              126.81                                                                                   d.sub.8                                                                             4.5                                                   S      --                                                                                       d.sub.9                                                                             4.5                                                   r.sub.9                                                                              -126.81                                                                                  d.sub.10                                                                            3.2  N.sub.5                                                                            1.4914                                                                              ν.sub.5                                                                         57.8                             r.sub.10                                                                             -63.23                                                                                   d.sub.11                                                                            3.6                                                   r.sub.11                                                                             -19.53                                                                                   d.sub.12                                                                            2.2  N.sub.6                                                                            1.6830                                                                              ν.sub.6                                                                         31.5                             r.sub.12                                                                             -29.83                                                                                   d.sub.13                                                                            0.8                                                   r.sub.13                                                                             -46.13                                                                                   d.sub.14                                                                            6.5  N.sub.7                                                                            1.7440                                                                              ν.sub.7                                                                         44.9                             r.sub.14                                                                             -26.76                                                                                   d.sub.15                                                                            0.6                                                   r.sub.15 *                                                                           -226.47                                                                                  d.sub.16                                                                            2.5  N.sub.8                                                                            1.5840                                                                              ν.sub.8                                                                         31.0                             r.sub.16 *                                                                           2668.30                                                                           Σd = 47.8                                                    f.sub.1 /f.sub.4 = -1.415                                                                         r.sub.3 /r.sub.6 = 1.37                                   N.sub.2 -N.sub.3 = 0.061                                                                          ν.sub.2 -ν.sub.3 = 13.41                            ______________________________________                                    

                                      TABLE 12 (b)                                __________________________________________________________________________    [Examp1e 12]                                                                  Aspherica1 coefficient                                                        __________________________________________________________________________    r.sub.1 :                                                                        A.sub.2 = 0.0                                                                              A.sub.3 = 0.0                                                                              A.sub.4 = -0.31643 × 10.sup.-7                A.sub.5 = 0.0                                                                              A.sub.6 = -0.70937 × 10.sup.-11                                                      A.sub.7 = 0.0                                       A.sub.8 = -0.96721 × 10.sup.-14                                                      A.sub.9 = 0.0                                                                              A.sub.10 = 0.10735 × 10.sup.-15               A.sub.11 = 0.0                                                                             A.sub.12 = 0.0                                                                             A.sub.13 = 0.0                                      A.sub.14 = 0.0                                                                             A.sub.15 = 0.0                                                                             A.sub.16 = 0.0                                   r.sub.2 :                                                                        A.sub.2 = 0.0                                                                              A.sub.3 = 0.0                                                                              A.sub.4 = 0.16835 × 10.sup.-17                A.sub.5 = 0.0                                                                              A.sub.6 = 0.77078 × 10.sup.-18                                                       A.sub.7 = 0.0                                       A.sub.8 = 0.38007 × 10.sup.-18                                                       A.sub.9  = 0.0                                                                             A.sub.10 = 0.44203 × 10.sup.-16               A.sub.11 = 0.0                                                                             A.sub.12 = 0.20398 × 10.sup.-18                                                      A.sub.13 = 0.0                                      A.sub.14 = 0.0                                                                             A.sub.15 = 0.0                                                                             A.sub.16 = 0.0                                   r.sub.15 :                                                                       A.sub.2 = 0.0                                                                              A.sub.3 = 0.0                                                                              A.sub.4 = -0.16835 × 10.sup.-17               A.sub.5 = 0.0                                                                              A.sub.6 = -0.77078 × 10.sup.-18                                                      A.sub.7 = 0.0                                       A.sub.8 = -0.38007 × 10.sup.-18                                                      A.sub.9 = 0.0                                                                              A.sub.10 = -0.44203 × 10.sup.-16              A.sub.11 = 0.0                                                                             A.sub.12 = -0.20398 × 10.sup.-18                                                     A.sub.13 = 0.0                                      A.sub.14 = 0.0                                                                             A.sub.15 = 0.0                                                                             A.sub.16 = 0.0                                   r.sub.16 :                                                                       A.sub.2 = 0.0                                                                              A.sub.3 = 0.0                                                                              A.sub.4 =  0.31643 × 10.sup.-7                A.sub.5 = 0.0                                                                              A.sub.6 = 0.70937 × 10.sup.-11                                                       A.sub.7 = 0.0                                       A.sub.8 = 0.96721 × 10.sup.-14                                                       A.sub.9 = 0.0                                                                              A.sub.10 = -0.10735 × 10.sup.-15              A.sub.11 = 0.0                                                                             A.sub.12 = 0.0                                                                             A.sub.13 = 0.0                                      A.sub.14 = 0.0                                                                             A.sub.15 = 0.0                                                                             A.sub.16 = 0.0                                   __________________________________________________________________________

In the foregoing description of the first to third embodiments, theconditional inequalities (3), (4) and (6) to (15) have been describedwith reference to the lenses positioned on the object side of thediaphragm. However, since the wide angle lens system of the embodimentsare symmetrical with respect to the diaphragm, it is to be noted thatthe lenses on the image side of the diaphragm of course similarlysatisfy such inequalities.

Moreover, in all of the Examples 1 to 12, a lens element having a convexsurface at one side and a concave surface at another side is a meniscuslens

Although the present invention has been fully described by the way ofexamples with reference to the accompanying drawings, it is to be notedthat various changes and modifications will be apparent to those skilledin the art. Therefore, unless otherwise such changes and modificationsdepart from the scope of the present invention, they should be construedas being included therein.

What is claimed is:
 1. A wide angle lens system comprising, from theobject sidea first lens element of a negative refractive power having anaspherical surface, a second lens element of a positive refractivepower, a third lens element of a negative refractive power, a fourthlens element of a positive refractive power, a diaphragm, a fifth lenselement of a positive refractive power, a sixth lens element of anegative refractive power, a seventh lens element of a positiverefractive power, and a eighth lens element of a negative refractivepower having an aspherical surface which is in rotation symmetry withthe aspherical surface of the first lens element with respect to thediaphragm.
 2. A wide angle lens system as claimed in claim 1, whereinthe aspherical surfaces of the first and eighth lens elements are soshaped that the refractive power increases in the negative directionwith an increase in the distance from the optical axis.
 3. A wide anglelens system for use in a copying machine, the lens system comprising,from the object side,a first lens element of a negative refractive powerhaving an aspherical surface, a second lens element consisting of apositive meniscus lens element having a convex surface faced to theobject side, a third lens element consisting of a negative meniscus lenselement having a convex surface faced to the object side, a fourth lenselement consisting of a positive meniscus lens element having a convexsurface faced to the object side, a diaphragm, a fifth lens elementbeing symmetrical with the fourth lens element with respect to thediaphragm, a sixth lens element being symmetrical with the third lenselement with respect to the diaphragm, a seventh lens element beingsymmetrical with the second lens element with respect to the diaphragm,and a eighth lens element being arranged symmetrically with the firstlens element and shaped to have an aspherical surface which is inrotation symmetry with the aspherical surface of the first lens elementwith respect to the diaphragm.
 4. A wide angle lens system as claimed inclaim 3, wherein the aspherical surfaces of the first and eighth lenselements are so shaped that the refractive power increases in thenegative direction with an increase in the distance from the opticalaxis.
 5. A wide angle lens system as claimed in claim 3, wherein thelens system fulfills the following condition,

    r4≧r5

r4: the radius of curvature of the diaphragm side surface of the secondlens element r5: the radius of curvature of the object side surface ofthe third lens element.
 6. A wide angle lens system as claimed in claim3, wherein the lens system fulfills the following condition,

    -2.5f<f1<-1.0f

f1: the focal length of the first lens element f: the focal length ofthe entire lens system.
 7. A wide angle lens system as claimed in claim3, wherein both of the first and eighth lens elements are made ofsynthetic resin.
 8. A wide angle lens system comprising, from the objectside,a first lens unit consisting of a negative lens element, a secondlens unit consisting of a positive meniscus lens element having a convexsurface faced to the object side and a negative meniscus lens elementhaving a concave surface faced to the image side, a third lens unitconsisting of a positive meniscus lens element having a convex surfacefaced to the object side, a diaphragm, a fourth lens unit beingsymmetrical with the third lens unit with respect to the diaphragm, afifth lens unit being symmetrical with the second lens unit with respectto the diaphragm, and a sixth lens unit being symmetrical with the firstlens unit with respect to the diaphragm, wherein the lens systemfulfilling the following condition,

    r4≧r5

r4: the radius of curvature of the diaphragm side surface of thepositive meniscus lens element of the second lens unit r5: the radius ofcurvature of the object side surface of the negative meniscus lenselement of the third lens unit.
 9. A wide angle lens system as claimedin claim 8, wherein the lens system fulfills the following condition,

    -2.5f<f1<-1.0f

f1: the focal length of the negative lens element of the first lens unitf: the focal length of the entire lens system.
 10. A wide angle lenssystem as claimed in claim 8, wherein the lens system fulfills thefollowing condition,

    1.0<r3/r6<1.5

r3: the radius of curvature of the object side surface of the positivemeniscus lens element of the second lens unit r6: the radius ofcurvature of the diaphragm side surface of the negative meniscus lenselement of the third lens unit.
 11. A wide angle lens system as claimedin claim 9, wherein the lens system fulfills the following condition,

    1.0<r3/r6<1.5

r3: the radius of curvature of the object side surface of the positivemeniscus lens element of the second lens unit r6: the radius ofcurvature of the diaphragm side surface of the negative meniscus lenselement of the third lens unit.
 12. A wide angle lens system as claimedin claim 8, wherein the lens system fulfills the following conditions,

    N2-N3>0.05

    ν2-ν3>6.0

N2: the refractive index of the positive meniscus lens element of thesecond lens unit N3: the refractive index of the negative meniscus lenselement of the second lens unit .sup.ν 2: the Abbe number of thepositive meniscus lens element of the second lens unit .sup.ν 3: theAbbe number of the negative meniscus lens element of the second lensunit.
 13. A wide angle lens system comprising, from the object side,afirst lens unit consisting of a negative lens element of syntheticresin, a second lens unit consisting of a positive meniscus lens elementhaving a convex surface faced to the object side and a negative meniscuslens element having a concave surface faced to the image side, a thirdlens unit consisting of a positive meniscus lens element of syntheticresin having a convex surface faced to the object side, a diaphragm, afourth lens unit being symmetrical with the third lens unit with respectto the diaphragm, a fifth lens unit being symmetrical with the secondlens unit with respect to the diaphragm, and a sixth lens unit beingsymmetrical with the first lens unit with respect to the diaphragm. 14.A wide angle lens system as claimed in claim 13, wherein the first,third, fourth and sixth lens units are so arranged as to correct theshift of the image point due to a variation in temperature.
 15. A wideangle lens system as claimed in claim 13, wherein the lens systemfulfills the following condition,

    -1.6<f1/f4<-0.95

f1: the focal length of the negative lens element of the first lens unitf4: the focal length of the positive meniscus lens element of the thirdlens unit.
 16. A wide angle lens system as claimed in claim 13, whereinthe lens system fulfills the following condition,

    1.0<r3/r6<1.5

r3: the radius of curvature of the object side surface of the positivemeniscus lens element of the second lens unit r6: the radius ofcurvature of the diaphragm side surface of the negative meniscus lenselement of the third lens element.
 17. A wide angle lens system asclaimed in claim 13, wherein the lens system fulfills the followingconditions,

    N2-N3>0.05

    ν2-ν3>6.0

N2: the refractive index of the positive meniscus lens element of thesecond lens unit N3: the refractive index of the negative meniscus lenselement of the second lens unit .sup.ν 2: the Abbe number of thepositive meniscus lens element of the second lens unit .sup.ν 3: theAbbe number of the negative meniscus lens element of the second lensunit.
 18. A wide angle lens system as claimed in claim 13, wherein thenegative lens element of the first lens unit has an aspherical surface,while the negative lens element of the sixth lens unit has an asphericalsurface which is in rotation symmetry with the aspherical surface of thefirst lens unit with respect to the diaphragm.